[GHC] #3208: Type family panic (taking the IdInfo of a coercion variable)

[GHC]

#3208: Type family panic (taking the IdInfo of a coercion variable)
-------------------------------+--------------------------------------------
  Reporter:  simonpj           |          Owner:  chak            
      Type:  bug               |         Status:  new             
  Priority:  normal            |      Milestone:  6.12 branch     
 Component:  Compiler          |        Version:  6.10.2          
  Severity:  normal            |       Keywords:                  
Difficulty:  Unknown           |       Testcase:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
-------------------------------+--------------------------------------------
 Jan Jakubuv found [http://www.haskell.org/pipermail/glasgow-haskell-
 users/2009-May/017147.html this]:
 {{{
 {-# OPTIONS -fglasgow-exts #-}
 module Foo where

 class SUBST s where
     type STerm s

 class OBJECT o where
     type OTerm o
     apply :: (SUBST s, OTerm o ~ STerm s) => s -> o

 fce' f = fce . apply $ f

 fce f = fce' f
 }}}
 yields, with GHC 6.10 or the HEAD:
 {{{
     ghc: panic! (the 'impossible' happened)
       (GHC version 6.10.2 for i386-unknown-linux):
             idInfo co{v agz} [tv]
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3208>
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